This invention pertains to the art of electronic control systems for electrically powered devices and more particularly to an electronic control system for a refrigerator.
The invention is particularly applicable to an electronic control system for a refrigerator to provide a self-adjusting defrost interval whereby the time period for a defrost operation is maintained within a preferred preselected time period. However, it will be appreciated to those skilled in the art that the invention can be readily adapted for use in other environments as, for example, where similar control systems are employed to maintain a preselected temperature and to avoid the accumulation of frost on an evaporator coil of a cooling system.
Accumulation of frost on an evaporator coil of a refrigeration system is a well known problem for which various forms and types of defrost systems have heretofore been suggested and employed all with varying degrees of success. Known technology includes mechanical controls to run the compressor and defrost functions of a refrigerator by electromechanical temperature sensing and motor-geared timing functions. The defrost function was a constant-timed function and occured after a fixed amount of compressor run time.
It is also known to employ electronic control systems which provide an adaptive defrost operation to vary the time period of a defrost operation or alternatively vary the time period of the interval between defrost operations. Such adaptive defrost control systems have typically involved complicated control circuitry which consider a variety of factors including the number and duration of freezer and fresh food door openings, the temperature of the evaporator coil at the beginning of the defrost operation, the duration of the previous defrosting operation, and the total accumulated compressor run time since the previous defrost operation.
For any refrigeration control system there are three primary design objectives. The first is dependability and durability. Since it is intended that the control system will operate continuously, it is necessary that the system be designed with a substantial mean time to failure. Prior known electromechanical control systems or complicated electronic control systems have suffered from the problems of a mean time to failure which has either been commercially unacceptable or was commonly recognized as having a need for substantial improvement. The second overall design objective is simplicity in design and operation. Simplicity in design goes hand-in-hand with durability and dependability but also facilitates ease of manufacture and service. The more complicated prior known control systems which lacked simplicity of design were particularly more costly and difficult to manufacture and similarly more difficult to service. The third overall design objective is cost in manufacture and efficiency in operation. A control system which is more economical to manufacture due to minimization of control components and which provides improved efficiency of operation comprises an improved control system over the more expensive prior known systems.
The present invention contemplates a new and improved refrigeration control system which overcomes the problems of prior known systems and which satisfies the design objectives for such control systems to provide an electronic refrigeration control which is simple in design, economical to manufacture and operate, and which provides optimum efficiency in evaporator coil defrosting and power economy performance by defrosting only when the need exists.